Details

The current yaml::Input constructor takes a StringRef of data as its
first parameter, discarding any filename information that may have been
present when a YAML file was opened. Add an alterate yaml::Input
constructor that takes a MemoryBufferRef, which can have a filename
associated with it. This leads to clearer diagnostic messages.

This isn't part of LLVM I usually hack on, but I just wanted to comment to say:

I've manually verified this patch applies cleanly to top of tree and all checks pass

The patch looks good to me, and addresses the final nits from @arphaman in the previous revision. The only other changes vs the previous revision seems to be the removal of CurrentNode from the initialiser list as the field now has a default initialiser (as of rL305969).